The present invention relates generally to forming coatings adhered to steel pipes to waterproof and protect the pipes against corrosion, and more particularly to an improved method for coating steel pipe with coal tar enamel, and to the products thereof.
As further background, steel pipe is commonly used to convey petroleum-based materials such as gas, oil and water. In service, of course, it is necessary that the steel pipe utilized be resistant to penetration by moisture which might facilitate corrosion of the steel and/or lead to contamination or loss of the material conveyed. For this reason, it is an adopted practice to coat steel pipe with a water-resistant bituminous material such as coal tar enamel. In this regard, coal tar enamel itself does not possess the properties necessary for sufficient direct bonding to steel pipe under relatively convenient processing conditions to meet the demands in industry. Therefore, a primer coat of chlorinated rubber has usually been applied to the steel pipe, followed by coating with the coal tar enamel to provide the overall waterproofed pipe.
In the steel pipe coating industry, waterproofing processes must desirably employ readily available and inexpensive materials which require as little handling as possible. In addition, processing steps should be convenient and processing time must be kept to a minimum. On the other hand, the resulting waterproof coating must survive a battery of tests in order to provide acceptable service. For example, industry has adopted several tests for the integrity of the coating including those for resistance to heat, cathodic disbondment, impact, and hot water.
In the face of these stringent economic and technical demands, there exists a need for improved methods for forming waterproof coatings on steel pipes, and improved products resultant of such methods. The instant invention addresses these needs.